U.S. patent application number 16/539706 was filed with the patent office on 2021-02-18 for hingeless helicopter rotor with high stiffness and low drag configuration.
The applicant listed for this patent is LOCKHEED MARTIN CORPORATION. Invention is credited to Pedro L. Cabrera, Kenneth F. Deyo, David N. Schmaling.
Application Number | 20210047024 16/539706 |
Document ID | / |
Family ID | 1000004955609 |
Filed Date | 2021-02-18 |
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United States Patent
Application |
20210047024 |
Kind Code |
A1 |
Cabrera; Pedro L. ; et
al. |
February 18, 2021 |
HINGELESS HELICOPTER ROTOR WITH HIGH STIFFNESS AND LOW DRAG
CONFIGURATION
Abstract
A hub assembly for a rotary wing aircraft having a rotor shaft
which rotates about a rotational axis includes: a hub extender arm
coupled to the rotor shaft; a pitch bearing that is disposed within
and connected to the hub extender arm; and a rotor blade assembly
having an inboard section disposed within the hub extender arm and
connected to the pitch bearing; wherein the hub extender arm has an
inboard cross-sectional area where coupled to the rotor shaft that
is greater than an outboard cross-sectional area where coupled to
the pitch bearing.
Inventors: |
Cabrera; Pedro L.; (West
Haven, CT) ; Schmaling; David N.; (Southbury, CT)
; Deyo; Kenneth F.; (Thomaston, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LOCKHEED MARTIN CORPORATION |
Bethesda |
MD |
US |
|
|
Family ID: |
1000004955609 |
Appl. No.: |
16/539706 |
Filed: |
August 13, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64C 27/10 20130101;
B64C 11/10 20130101 |
International
Class: |
B64C 11/10 20060101
B64C011/10; B64C 27/10 20060101 B64C027/10 |
Claims
1. A hub assembly for a rotary wing aircraft having a rotor shaft
which rotates about a rotational axis, the hub assembly comprising:
a hub extender arm coupled to the rotor shaft; a pitch bearing that
is disposed within and connected to the hub extender arm; and a
rotor blade assembly having an inboard section disposed within the
hub extender arm and connected to the pitch bearing; wherein the
hub extender arm has an inboard cross-sectional area where coupled
to the rotor shaft that is greater than an outboard cross-sectional
area where coupled to the pitch bearing.
2. The hub assembly according to claim 1, wherein the rotor blade
assembly has an outboard cross-sectional area at an outboard end of
the hub extender arm that is greater than an inboard
cross-sectional area at an inboard end of the hub extender arm.
3. The hub assembly according to claim 1, wherein the rotor blade
assembly comprises a blade grip coupled to a rotor blade and at
least a portion of the blade grip is disposed within the hub
extender arm.
4. The hub assembly according to claim 3, wherein at least one of
the hub extender arm and the blade grip comprises an aramid fiber
and/or a graphite and epoxy combination.
5. The hub assembly according to claim 3, further comprising a
pitch horn for controlling the pitch of the rotor blade.
6. The hub assembly according to claim 3, wherein the hub assembly
comprises an upper hub assembly having an upper hub extender arm
and an upper rotor blade assembly and a lower hub assembly having a
lower hub extender arm and a lower rotor blade assembly.
7. The hub assembly according to claim 6, wherein the pitch horn of
the lower blade assembly is coupled to the blade grip and disposed
in an opening in the lower hub extender arm.
8. The hub assembly according to claim 6, wherein the pitch horn of
the upper blade assembly is coupled to the pitch bearing and
disposed within the rotor shaft.
9. The hub assembly according to claim 8, wherein the pitch bearing
comprises: an inboard pitch bearing disposed within the hub
extender arm and coupled to the hub extender arm and the blade
grip; and an outboard pitch bearing disposed within the hub
extender arm and coupled to the hub extender arm and the blade
grip.
10. The hub assembly according to claim 9, wherein the pitch horn
of the upper blade assembly is coupled to the inboard pitch
bearing.
11. The hub assembly according to claim 6, further comprising an
upper fairing covering the upper hub extender arm and a lower
fairing covering the lower hub extender arm.
12. The hub assembly according to claim 11, further comprising a
middle fairing disposed between the upper fairing and the lower
fairing and surrounding the rotor shaft.
13. The hub assembly according to claim 12, further comprising an
interface fairing coupled to each of the upper and lower fairings
and a corresponding rotor blade of the rotor blade assembly.
14. The hub assembly according to claim 1, wherein the rotary wing
aircraft comprises a rigid rotor system.
15. A rotary wing aircraft comprising: an airframe; a gear box
coupled to the airframe; a rotor shaft coupled to the gear box; a
hub extender arm coupled to the rotor shaft; a pitch bearing that
is disposed within and connected to the hub extender arm; and a
rotor blade assembly having an inboard section disposed within the
hub extender arm and connected to the pitch bearing; wherein the
hub extender arm has an inboard cross-sectional area where coupled
to the rotor shaft that is greater than an outboard cross-sectional
area where coupled to the pitch bearing.
16. The rotary wing aircraft according to claim 15, wherein the
rotor blade assembly has an outboard cross-sectional area at an
outboard end of the hub extender arm that is greater than an
inboard cross-sectional area at an inboard end of the hub extender
arm.
17. The rotary wing aircraft according to claim 15, wherein the
rotor blade assembly comprises a blade grip coupled to a rotor
blade and at least a portion of the blade grip is disposed within
the hub extender arm.
18. The rotary wing aircraft according to claim 17, wherein at
least one of the hub extender arm and the blade grip comprises an
aramid fiber and/or a graphite and epoxy combination.
19. The rotary wing aircraft according to claim 15, wherein the hub
assembly comprises an upper hub assembly having an upper hub
extender arm and an upper rotor blade assembly and a lower hub
assembly having a lower hub extender arm and a lower rotor blade
assembly.
20. The rotary wing aircraft according to claim 15, wherein the
pitch bearing comprises: an inboard pitch bearing disposed within
the hub extender arm and coupled to the hub extender arm and the
blade grip; and an outboard pitch bearing disposed within the hub
extender arm and coupled to the hub extender arm and the blade
grip.
Description
BACKGROUND
[0001] The embodiments disclosed herein relate to a connection of
rotor of a rotary wing aircraft to a rotor hub assembly, and more
particularly to the connection having high stiffness and low
aerodynamic drag.
[0002] The flight capabilities of rotary-wing aircrafts make them
effective for a wide variety of missions due to their ability to
take-off and land vertically in addition to their ability to hover.
The rotating blades necessary for these abilities, however, require
that their connections to a rotor shaft be able to withstand high
centrifugal forces as the blades rotate, be able to change the
pitch of the blades as they rotate, be able to achieve high bending
stiffness, as well as provide low aerodynamic drag. Existing
connections that can withstand the centrifugal forces present a
larger than desired cross-sectional area that is susceptible to
drag, thereby decreasing the efficiency of the rotary wing aircraft
in flight.
BRIEF DESCRIPTION
[0003] Disclosed is a hub assembly for a rotary wing aircraft
having a rotor shaft which rotates about a rotational axis. The hub
assembly includes: a hub extender arm coupled to the rotor shaft; a
pitch bearing that is disposed within and connected to the hub
extender arm; and a rotor blade assembly having an inboard section
disposed within the hub extender arm and connected to the pitch
bearing; wherein the hub extender arm has an inboard
cross-sectional area where coupled to the rotor shaft that is
greater than an outboard cross-sectional area where coupled to the
pitch bearing.
[0004] Also disclosed is a rotary wing aircraft. The rotary wing
aircraft includes: an airframe; a gear box coupled to the airframe;
a rotor shaft coupled to the gear box; a hub extender arm coupled
to the rotor shaft; a pitch bearing that is disposed within and
connected to the hub extender arm; and a rotor blade assembly
having an inboard section disposed within the hub extender arm and
connected to the pitch bearing; wherein the hub extender arm has an
inboard cross-sectional area where coupled to the rotor shaft that
is greater than an outboard cross-sectional area where coupled to
the pitch bearing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The following descriptions should not be considered limiting
in any way. With reference to the accompanying drawings, like
elements are numbered alike:
[0006] FIG. 1 is a perspective view of a rotary wing aircraft
having a rigid rotor system;
[0007] FIG. 2 is a detailed view of the rigid rotor system having a
rotor hub assembly;
[0008] FIG. 3 is a perspective view of the rigid rotor system;
[0009] FIG. 4 is a perspective view of a hub extender arm connected
to a rotor blade assembly;
[0010] FIG. 5 is a side view of the hub extender arm having box
walls;
[0011] FIG. 6 is a perspective view of a blade grip;
[0012] FIG. 7 is a side cross-sectional view of an upper blade grip
disposed inside of the hub extender arm;
[0013] FIG. 8 is a top cross-sectional view of a lower blade grip
disposed inside of the hub extender arm; and
[0014] FIG. 9 is a perspective view of the rigid rotor system
covered with aerodynamic fairings.
DETAILED DESCRIPTION
[0015] A detailed description of one or more embodiments of the
disclosed apparatus and method are presented herein by way of
exemplification and not limitation with reference to the
Figures.
[0016] FIG. 1 illustrates an exemplary vertical takeoff and landing
(VTOL) rotary-wing aircraft 10 having a dual, counter-rotating,
coaxial rotor system 12 which rotates about an axis of rotation A.
The aircraft 10 includes an airframe 14 which supports the dual,
counter rotating, coaxial rotor system 12 as well as an optional
translational thrust system T which provides translational thrust
generally parallel to an aircraft longitudinal axis L. Although a
particular aircraft configuration is illustrated in the disclosed
embodiment, other counter-rotating, coaxial rotor systems will also
benefit from the present invention. In one or more embodiments, the
coaxial rotor system 12 is a rigid rotor system (i.e., hingeless)
in which mechanical components enable each rotor blade of the rotor
system to change pitch as the blades rotate. The rigid rotor system
in general does not include mechanical components for enabling flap
movement and lead/lag movement of the blades. Any flap movement or
lead/lag movement is due to bending of the blades.
[0017] A main gearbox 26, which may be located above the aircraft
cabin, drives the rotor system 12. The translational thrust system
T may be driven by the same main gearbox 26 which drives the rotor
system 12. The main gearbox 26 is driven by one or more engines
(illustrated schematically at E). As shown, the main gearbox 26 may
be interposed between the gas turbine engines E, the rotor system
12 and the translational thrust system T.
[0018] Referring to FIG. 2, the dual, counter-rotating, coaxial
rotor system 12 includes an upper rotor system 16 and a lower rotor
system 18. Each rotor system 16, 18 includes a plurality of rotor
blade assemblies 20 mounted to a rotor hub assembly 22, 24 for
rotation about a rotor axis of rotation A. The shown upper rotor
system 16 and lower rotor system 18 include corresponding hub
fairings which surround and reduce drag for the rotor hub assembly
22, 24. A plurality of the main rotor blade assemblies 20 project
radially outward from the hub assemblies 22, 24. Any number of main
rotor blade assemblies 20 may be used with the rotor system 12.
While not shown, a fairing may be disposed between upper rotor
system 16 and lower rotor system 18 to reduce drag in this
region.
[0019] Referring now to FIGS. 3 and 4, at least one of the rotor
blade assemblies 20 of the rotor system 12 includes a rotor blade
30 and a blade grip 31. A rotor shaft 36 rotates to rotate the
rotor hub assemblies 22, 24. In the illustrated non-limiting
embodiment, the main rotor system 12 is a rigid rotor system. A hub
arm extender 32 extends from the rotor shaft 36. The rotor shaft 36
includes a hub arm extender connector 33 to connect the hub arm
extender 32 to the rotor shaft 36. In one or more embodiments, the
connector 33 uses bolts 34 to connect to the hub arm extender 32
and shaft 36. The hub extender 32 includes upper, lower, and side
walls that define an inboard end opening and an outboard end
opening. The upper wall is the wall farthest from the fuselage 14
along the axis of rotation A for the shaft 36, and the lower wall
is between the upper wall and the fuselage 14 along the axis of
rotation A for the shaft 36. The blade grip 31 is disposed inside
the hub arm extender 32 and attached to an inner race of one or
more pitch bearings 41, 42 that enables the blade grip 31 and thus
the rotor blade 30 to change pitch about a pitch axis as the rotor
blade 30 rotates about the rotational axis A. In one or more
embodiments, the blade grip 31 is coupled to the rotor blade 30
just outside of the hub extender arm 32. The term "inboard" relates
to closest to the rotor shaft 36, while the term "outboard" relates
to being further away from the rotor shaft 36. An outer race of the
pitch bearings 41, 42 in turn is attached to the hub arm extender
32 or the rotor shaft 36. A lower pitch horn 35 is attached to the
blade grip 31 in order to control the pitch of the blade 30 as it
rotates about the rotational axis A. A pitch control rod 37 is
connected to the lower pitch horn 35. In one or more embodiments,
an end of the pitch control rod 37 is coupled to a swashplate (not
shown) to provide the appropriate pitch control inputs.
[0020] FIG. 4 is a perspective view of the hub extender arm 32
connected to the blade grip 31. In the embodiment of FIG. 4, the
blade grip 31 is disposed within the hub arm extender 32 and is
connected to an inboard pitch bearing 41 and an outboard pitch
bearing 42. The pitch bearings 41 and 42 enable the blade 30 to
change pitch as the blade 30 rotates about the rotational axis A
and also provide the necessary centripetal force to keep the blade
assembly 20 attached to the hub arm extender 32 and thus to the
rotor shaft 31 as the rotor blade 30 rotates.
[0021] The rotary-wing aircraft 10 requires high flap-wise
stiffness (e.g., up and down stiffness with respect to horizontal
flight of the rotary-wing aircraft 10) to decrease unwanted
vibrations during flight and also requires low aerodynamic drag of
the rotor hub assembly 22, 24 to increase efficiency. Typically,
these two requirements are in direct conflict with one another.
However, disposing the blade grip 31 within the hub extender arm 32
as disclosed herein provides for the needed high flap-wise
stiffness to decrease unwanted vibrations during flight and at the
same time lower the cross-sectional area of the rotor hub assembly
22, 24 in order to decrease aerodynamic drag. In aspects of the
invention, the rotor hub assembly 22, 24 can be designed to be as
stiff as required while the height of the rotor hub assembly 22, 24
can be minimized. The flapping stiffness of the rotor blade
assembly 20 is primarily driven by stiffness of the stationary
(with respect to the rotor shaft 36) hub extender arm 32 and the
pitching blade grip 31. These two components in one or more
embodiments are connected to one another via two pitch bearings 41,
42 (one inboard and one outboard). The embodiments of the rotor hub
assembly 22, 24 configuration as disclosed herein resolves the
conflicting requirement of high stiffness and low drag by
recognizing that the hub extender arm 32 and the blade grip 31
react the rotor blade 30 loads in different manners. The blade grip
31 is exposed to the highest blade bending moment at the outboard
attachment and the moment decreases inboard reaching zero at the
inboard pitch bearing 41. From a structures perspective, the blade
grip 31 behaves as cantilever beam where a shear load is applied at
the inboard end and it is fixed at the outboard end. On the other
hand, the moment carried by the hub extender arm 32 starts at zero
at the outboard pitch bearing 42 and grows in magnitude to a
maximum value at the inboard pitch bearing 41. As a structure, it
acts as a cantilever beam with a shear load applied at the outboard
pitch bearing 42 and it is fixed at the inboard bearing 41. The
fact that the moments carried by these two components peak at
opposite ends allow for a nested design where one part can get
bigger without driving the size of the other part.
[0022] In other designs, the blade grip goes over the hub extender
arm. This means that as the hub extender arm gets bigger inboard to
achieve the higher stiffness the blade grip must get bigger to
clear the hub extender arm. This arrangement results in an
inefficient structure since the moment carried by the blade grip
dictates the blade grip tube should be smaller inboard not bigger.
This has resulted in a design that either does not meet the
stiffness requirement or has a taller hub than is required to carry
the loads and thus has increased aerodynamic drag at the hub
assembly.
[0023] According to aspects of the invention, the rotor hub
assembly 22, 24 allows a rotor design with high flatwise stiffness
while minimizing the drag of the rotor hub assembly 22, 24. This
design takes advantage of the fact that the hub extender arm 32 and
the blade grip 31 carry the rotor blade 30 loads in different
manners. It recognizes that from a structures perspective the hub
extender arm 32 can start with a small cross section outboard and
become larger as the cross-section moves inboard. On the other
hand, the blade grip 31 can start with a large cross section
outboard and get smaller as the cross-section moves inboard. The
fact that the two structures are exposed to moments that increase
in opposite directions allows for a nested design with the
attributes of high flap-wise stiffness and minimized rotor hub
assembly 22, 24 height and drag. In FIG. 5, a cross-sectional area
of the hub extender arm 32 (that includes structural box walls 50)
in a plane that is perpendicular to a longitudinal axis of the hub
extender arm 32 at 51 (i.e., inboard plane) is greater than the
cross-sectional area of that hub extender arm 32 in a plane at 52
(i.e., outboard plane). Assuming that the structural box walls 50
have uniform thickness, the larger cross-sectional area provides
for more flap-wise stiffness than the smaller cross-sectional area.
Conversely, the blade grip 31 can have a smaller cross-sectional
area towards the inboard end of the blade grip 31 relative to the
cross-sectional area towards the outboard end of the blade grip 31
assuming uniform thickness of a longitudinal structural element of
the blade grip 31. The varied cross-sectional areas of both the hub
extender arm 32 and the blade grip 31 provides the advantage of
reducing the weight of these components and increasing the
efficiency of the rotary-wing aircraft 10. In one or more
embodiments, the hub extender arm 32 has a cross-sectional area in
a first inboard plane that is greater than or equal to a
cross-sectional area in a first outboard plane and/or the inboard
section of the rotor blade assembly 20 has a cross-sectional area
in a second inboard plane that is less than or equal to a
cross-sectional area in a second outboard plane. In one or more
embodiments, the inboard and outboard planes perpendicular to the
longitudinal axis of the inboard section of the rotor blade
assembly 20. In one or more embodiments, the hub extender arm 32
has an inboard cross-sectional area where coupled to the rotor
shaft 36 that is greater than an outboard cross-sectional area
where coupled to the pitch bearing 42.
[0024] According to aspects of the invention, the hub extender arm
32 and/or the blade grip 31 can be made of a composite material
such as an aramid fiber (e.g., poly-paraphenylene terephthalamide
commonly known as Kevlar.RTM.) or a graphite/epoxy combination to
provide strength and light weight. In addition, making these
components with a composite material enables the cross-sectional
area and/or thickness of structural elements to be varied or
fine-tuned so that the flap-wise stiffness of these components
complements each other in the nested configuration.
[0025] FIG. 6 is a perspective view of the blade grip 31 that is
disposed inside of the hub extender arm 32 without being obscured
by the hub extender arm 32.
[0026] FIG. 7 is a side cross-sectional view of the blade grip 31
for the upper rotor system 16 disposed inside of the hub extender
arm 32. The embodiment of FIG. 7 includes an upper pitch horn 70
for changing the pitch of the blade grip 31 for the upper rotor
system 16 and thus the pitch of the rotor blade 30 as the blade 30
rotates. The upper pitch horn 70 extends into an interior space of
the rotor shaft 36 and is attached to an inboard pitch control
linkage (not shown) in that interior space.
[0027] FIG. 8 is a top cross-sectional view of the blade grip 31
that is disposed inside of the hub extender arm 32 for the lower
rotor system 18. In the embodiment of FIG. 8, a lower pitch horn 35
for the lower rotor system 18 is disposed external to the rotor
shaft 36. The lower pitch horn 35 is configured for changing the
pitch of the blade grip 31 for the lower rotor system 18 and thus
the pitch of the rotor blade 30 as the blade 30 rotates. As
illustrated in FIG. 8, the lower pitch horn 35 is attached to the
pitch control rod 37.
[0028] FIG. 9 is a perspective view of the rigid rotor system 12
covered with aerodynamic fairings. An upper hub fairing 91 covers
and may be coupled to the upper hub assembly 22 and a lower hub
fairing 92 covers and may be coupled to the lower hub assembly 24
such that there is no relative motion between the fairings 91, 92
and the hub assemblies 22, 24, respectively. The height of each of
the hub fairings 91 and 92 is reduced because each of the rotors 30
is disposed into the corresponding hub extender arm 32. Because the
height of the fairings 91 and 92 is reduced, the aerodynamic drag
of the fairings 91 and 92 is also reduced thereby increasing the
efficiency of the rotary-wing aircraft 10. To further decrease
aerodynamic drag, a middle fairing 93 is disposed about the rotor
shaft 36 between the upper fairing 91 and the lower fairing 92.
Aerodynamic drag may further be reduced by an interface fairing 94
coupled to each rotor blade 30 and a tip or edge of each
corresponding hub fairing.
[0029] Elements of the embodiments have been introduced w either
the articles "a" or "an." The articles are intended to mean that
there are one or more of the elements. The terms "including" and
"having" and the like are intended to be inclusive such that there
may be additional elements other than the elements listed. The
conjunction "or" when used with a list of at least two terms is
intended to mean any term or combination of terms. The term
"configured" relates one or more structural limitations of a device
that are required for the device to perform the function or
operation for which the device is configured. The terms "first" and
"second" do not denote a specific order but are intended to
distinguish elements.
[0030] The disclosure illustratively disclosed herein may be
practiced in the absence of any element which is not specifically
disclosed herein.
[0031] While the present disclosure has been described with
reference to an exemplary embodiment or embodiments, it will be
understood by those skilled in the art that various changes may be
made and equivalents may be substituted for elements thereof
without departing from the scope of the present disclosure. In
addition, many modifications may be made to adapt a particular
situation or material to the teachings of the present disclosure
without departing from the essential scope thereof. Therefore, it
is intended that the present disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this present disclosure, but that the present
disclosure will include all embodiments falling within the scope of
the claims.
* * * * *